Drilling mud



Patented Aug. 15, I950 UNITED STATES PATENT OFFICE 2,513,439 DRILLINGMUD Paul W. Fischer, Long Beach, and Raymond A. Rogers, Wilmington,Calif., assignors to Union Oil Company of California, Los Angeles,Calif.,

a corporation of California No Drawing. Application July 27, 1946,Serial No. 686,726

1'7 Claims.

'which other materials such as barium sulfate may be added in order toincrease its apparent specific gravity. The physical characteristics ofthese clay suspensions are largely determined by the properties of theindividual clay particles, most important of which are size, shape andsurface characteristics.

Until recently it has been considered that the principal functions of amud in drilling operations are three-fold: it should form a cake on thewall of the hole; it should retain in suspension the cuttings formed sothat the latter may be removed from the hole along with the mud; and itshould possess suflicient weight to overcome any pressure encounteredduring drilling. These functions are considered in more detail below.

One of the primary difliculties encountered in the drilling of wells isthat due to the sloughing or caving into the hole of the formationspenetrated. The use of a drilling mud is supposed to lessen the tendencyfor caving by mudding-off the formations, that is, forming a cake on thewalls of the hole. It is recognized, however, that drilling fluidsprepared from natural clays vary widely in their ability to preventsloughing of formations and that those fluids which form a thingelatinous cake on the walls of the hole and have a minimum tendency tolose water to the surrounding formations are the most desirable.

In order for drilling to proceed smoothly, means must be provided forcontinuously removing the cuttings from the hole and to this enddrilling mud is circulated through the hole. The mud must be ofsufliciently low viscosity to allow it to be readily pumped and itshould be thixotropic. Thixotropy is that property of colloidalsuspension which involves an increase in gel strength as a function ofthe time of quiescent standing. This property is valuable in that itprevents, to a large extent, the sedimentation of the cuttings in thehole during periods of suspended circulation. However, immediately after.-1.:.

violent agitation, such as is induced by the circulation of the mud,cuttings will settle a short distance and this fact is utilized fortheir removal in a settling tank provided for the purpose and in whichthe degree of agitation is sud- 5:.

Cil

blow-outs.

denly lowered to practically zero. Normally, a mud which has proper wallbuilding characteristics and is pumpable will have adequate thixotropicproperties.

Obviously, the total weight of a mud must be sufliciently great toprevent blow-outs from any high pressure formations that may beencoun-..

tered, but beyond this point, the need for greater weight isproblematical. A rapid reduction in the hydrostatic head maintained onformations, caused by a reduction in the specific weight of the mud orby permitting the level of the mud in the well to fall while removingthe drilling tools from the hole may cause dangerous caving. Therefore,mud is usually pumped into the well while removing the drill string inorder to maintain a substantially constant hydrostatic head on theformations being drilled and the mud gravity is always kept as constantas practical. In general, the practice has been to keep the weight ofmud onl sufliciently high to prevent It is common practice to increasethe specific gravity of a mud by adding insoluble materials of highdensity, such as for example, barium sulfate, iron oxide, etc. Becauseof their insolubility, the usual weighting agents employed have littleeffect on the performance characteristics of a mud.

Of the -various characteristics of a drilling mud, the most important isits tendency to lose Water to the formation. It has been found that thestructural strengths of most formations which are penetrated duringdrilling are sufficient to prevent the walls of the hole from caving,but that many such formations are weakened from being saturated or evenpartially saturated with water. Frequently such action causes sloughingof the formation into the hole with a resultant seizing of the drillpipe or tools so that they cannot be removed and costly fishing jobsresult. It is, therefore, of the greatest importance to prevent loss ofwater from the drilling mud to the formations drilled. The idealdrilling fluid should permit very little if any loss of water to theformation and should deposit only a relatively thin mud cake on thewalls of the hole.

As has been mentioned hereinabove, the most important physicalcharacteristic of a drilling mud is its ability to form a thinimpervious cake on the walls of the hole thereby sealing formationsagainst infiltration of water. The terms cake-forming and water-lossproperties, sealing properties and, as will be brought outherein below,filtration characteristics or filter rateare .of water, as cave-ins areliable to occur.

used synonymously throughout this specification to denote thischaracteristic.

A measure of the tendency for a mud to lose water to the formationsbeing drilled and to form a thin impervious cake upon the wall of thehole can be obtained by means of a simple filtration test. In fact, thescaling properties of the mud are almost entirely dependent upon thecharacter of the mud-cake formed when the latter is pressed against amembrane or filter permeable to water and are very largely independentofthe character of the membrane or filter employed. As a consequence, thefiltration rate of a mud becomes of prime importance in determining thequality of the mud.

The procedure for determining filtration rate is decribed in RecommendedPractice on Standard Field Procedure for Testing Drilling Fluids, A. P.I. Code No. 29, second edition, published July, 1942, page 11, andconsists in measuring the .total volume of filtrate water obtainedduring a given time inerval of pressure filtration. IPhe amount offiltrate obtained in thefirst five minutes of filtration can be used asan indication of the relative quality of various muds. A more accurateevaluation is obtained from the volume of filtrate collected inthe'first fifteen minutes .of filtration. Aneven better procedure is todetermine the total volume of -.filtrate in the first hour offiltration. Numerous correlations .between such tests and actualdrilling experience with the same muds have shown that the muds yieldinga total filtrate of less than 30 ml. in the first hours filtrationperiodare usually very satisfactory. On the other hand, muds yielding a totalfiltrate in excess of 45 ml. under similar circumstances have been founddangerous to use, particularly when drilling through formations whichare readilysoftened bypenetration Under some circumstances, particularlywhen drilling surface formations, or formations atmoderate depth, thepermissible maximum filtration rate of .the mud may be as high as about55 ml. of total filtrate in the first hour of filtration. ,A :mudwhichyields a total filtrate .of 30 ml. in the first hours filtrationperiod will yield about 7 ml. of filtrate in the first five minutes andabout 15 ml. of filtrate in the first fifteen minutes of filtration.Similarly a mud which yields a filtrateof 45 ml. in thefirst hour offiltration ,will give approximately 11 ml. inthefirst fivemin- .utes andabout 22 ml. in the first fifteen minutes of filtration. A mud which issatisfactory for drilling operations will under the conditions of thistest, deposit a filter cake of not overonequarter inch in thickness andor asoft, :plastic or gelatinous texture, ;whereas muds exhibitingunsatisfactory filter rates .tend to deposita thick, tough mud cake.Normally, as has already been mentioned hereinabove, muds possessingacceptable filtering characteristics form good mud cakes and, therefore,in practice only the ffiltering rate is ordinarily observed.

From the foregoing, it may be concluded that in preparing or treating adrilling mud in order to endow it with properties which will tend ,toinsure satisfactory performance in thefield, it is desirable'that thetreated mud when tested, as above described, yield a total filtrate ofnot over 55ml. in the first hour of filtration, and-preferably less than30ml. of filtrate, and that the deposited cake be preferably less thanonequarter inch in thickness and of a soft gelatinous texture.

It has also been observed that if the water losses from the drillingfiuid to the formations being drilled contains a dissolved salt ormixture of salts, such as for example sodium chloride and calciumchloride, in appreciable quantity, there is less tendency for swellingof the formation to occur. In'the production zone this is particularlyimportant and is reflected in an increased rate of production from thewell. Accordingly, inmany cases it is desirable to incorporate a salt,such as for example sodium chloride, in drilling mud to the extent Of 1%t0 "5% or as much as 10% by weight of the total mud, or even more.However, the addition of such quantities of a salt usually have anadverse effect upon the water loss characteristics of the mud and it isnecessary to control the performance characteristics of a salt-base mudby the addition of treating agents.

As has already been mentioned hereinabove, a mud-in order Lto .be;usable, must .be capable of being rea ily and ea l circ te -1hr m ans:of a pump such as is ordinarily emplcyed for the purpose in the field.Froma practical standpoint, it ,has been found that within certainlimits the more readilythe mud canbe-circu- .lated, the faster willdrilling proceed. With many muds :it has beenzobserved that'if theirMarsh funnel viscosities, as determinedby the 500 ml. in and .500 m1.out method, is-in excess of 55 seconds they may exhibitimpairedcircnlation rates. Onthe-otherhand, it has nowbeen observed thatcertain, materials When .addedi to control water loss may resultyin:mllds ,having viscosities in excess of 55. seconds :but whicharereadily pumpable in actual practice.

In so far as the drilling operation and .the subsequent production rateare concerned the -most important characte1'isticof ,a drilling mud isits filtering rate and the-viscosity of the mud need only be .suchthat-itispumpable. Throughout this specification and the claims,wherever the termsviscosity, :Marsh viscosity, apparent viscosity orfunnel viscosity are employed, they relate to the viscosity asdetermined by means of the above test, ,a description. of wl richean .befound in Recommended ,eEractice on ;Standard .Field Procedure forflestingsDrilling Fluids, A. P. :1. Code No. 29, second edition,published July 1942, page ,6, except :that 500,,ml. .of mud is measuredinto the funnel and the time determined for the 500ml. to runout.

Itis therefore, one of the robjectslof this invention .toprovide .for,a. treatment of :a drilling mud which will cause :the -:latter to :have.a .ifiltra ion rate of less than .zapproximatelylfi ml. andatgmostgnot'more than 55 ml. in thelfirst hour of filtration, said treated .mudhaving. a viscosity sufficiently ;-lo w so that :it is. lpumpable.

When the .aviscosity ,ofythe mud is sufficiently low topermit/tit;to.bereadilycirculatediand the filtration rate is within.theilimits describedhere; inabove, the. mud willordinarly possess:sufiicient thixotropic properties ';f or all practical. purposes.

It isanother obj ectof this inventionto prcvide' for a'treatmentofadrillingrnud containing an added inorganic resulting from the.reactionni an alkali metalor an ';allali n'e;,earth metalwith a strongmineral, acid-such was for example sodium chloride, potassium sulfate.and :calcium nitrate, said treatment :causing the -.salt+base' in thefirsthourgor filtration, said treated mud inepumpab e. V V

The term performance characteristics is herein used to include wallbuilding, water-loss and thixotropic properties and viscosity but doesnot refer to the specific gravity of the mud.

-- In the usual field operations, it is often necessary to form a cementplug in the hole and to subsequently drill through this plug, therebycontaminating the mud with cement. Mud which has been contaminated withcement is termed "cement-cut mud. It has been observed that such mudsusually possess poor performance characteristics in accordance with thequality definitions given hereinabove and that the greater thecontamination the poorer the quality. Cement-cut muds often become soviscous in character that it is difficult, and often impossible, tocirculate the contaminated material. This increase in apparent viscositymay impart "gas cutting tendencies to the muds, that is, prevent theescape of gas from the mud. and tend to prevent the proper release ofcuttings therefrom. Further, as will be discussed more fully later, suchmuds form thick, pervious cakes upon the wall of the hole which permitthe ready penetration of water into the formation.

Clays, which consist predominately of hydrated silicates of alumina,when suspended in water possess an appreciable electric charge, suchcharge in general being of a negative character. On the other hand,cement as is well known comprises a complex mixture of compounds ofcalcium, magnesium, iron, aluminum and silicon. Although it has not beenestablished beyond question and it is not desired to be bound by thetheory, it is believed that the poor performance characteristicsimparted by the presence of cement to an otherwise satisfactory drillingmud is due in part to the coagulation or flocculation of the negativelycharged clay particles by the polyvalent positively charged metallicions leached from the contaminating cement. Normally by far the largestproportion of the positive ions leached from cement are calcium ions.Muds may also become similarly contaminated during drilling operationsby coming in contact with penetrated formations which contain materials,such as gypsum, from which polyvalent metallic ions may be leached bythe aqueous phase of the drilling fluid.

Furthermore, depending upon the particular source, even the virgin claysemployed for preparing drilling muds may contain materials capable ofyielding polyvalent metallic ions when the clay is dispersed in water.

In any event, by whatever means the contamination may take place, itappears that the presence of polyvalent metallic ions either in solutionin the aqueous phase and/or in combination with the negatively chargedclay particles, is highly undesirable in that such a condition adverselyaffects the performance characteristics of the mud.

In the past when drilling muds have become contaminated or, in anyevent, when their apparent viscosities have become undesirably high, ithas frequently been the practice to remove the mud from the hole and todispose of it as useless material. Such practice involved a considerabledisposal problem and, furthermore, it entailed considerable expense forthe purchase of new mud. It has been the practice in some fields tolower the viscosity of cement-cut muds by the addition of water. In thepast this has been highly undesirable inasmuch as such muds normallyexhibited excessively high filter rates.

Muds reclaimed by means of chemical treatment, unless properlycontrolled, will not be of high quality nor will they alleviate thedifficulties encountered from the caving of formations. The reason forthis is that a treatment which merely control the viscosity of the mudis insufiicient unless attention has also been given to the cakeformingand water-loss properties of the mud and their importance.

It has now been found that drilling muds can be treated with certainreagents which will control both the viscosity and the filtration rateof the mud and that it is possible to add the reagents to the mud eitherafter the contamination has taken place or, in those cases where it isknown or expected that the mud is going to be contaminated byundesirable materials, such as for example, when it is anticipated thata cement plug will be drilled through and that the mud will then becomecontaminated with cement, the reagents can be added to the mud prior tosaid contamination. This latter type of treatment immunizes the mudagainst any substantial deterioration in its performance characteristicsupon subsequent admixing with the contaminating material, and in somecases it has been found that such contamination after the addition ofthe reagents which have now been discovered even improves theperformance characteristics of the mud. Furthermore, these reagents areso effective in controlling water loss that the viscosity if desired canbe controlled merely by the addition of water to the mud either beforeor after contamination with the cement or similar materials.Illustrative of this point it has been observed that when mud becomescontaminated with cement its viscosity and filtration rate becomesundesirably high, but that these factors can be reduced to desirablevalues by the addition to the contaminated mud of a mixture of aconcentrate comprising about 60% of a sodium salt of mahogany sulfonicacids and about 40% of lubricating oil, sodium gum karaya and water. Onthe other hand, by adding the mixture of a concentrate comprising about60 of a sodium salt of mahogany sulfonac acids and about 40% oflubricating oil, sodium gum karaya and water to the mud prior tocontamination with cement, the performance characteristics of the mudare improved, and upon the subsequent addition of cement the performancecharacteristics are still acceptable and in many cases may remainsubstantially unchanged or may even be improved.

It is another object of this invention to provide for a treatment of mudwhich will simultaneously control cake-forming and water lossproperties, the viscosity and the thixotropic properties of the mud andwhich will not markedly alter the specific gravity of the mud.

It is an additional object of this invention to provide for acombination treatment of muds comprising the addition of one or morematerials which will control the viscosity of the mud Without acceptablyaltering its cake-forming properties and a second material orcombination of materials which will control the cake-forming propertiesof the mud without acceptably controlling its viscosity.

It is also an object of this invention to provide for the pretreatmentof mud in order to render it immune to the effects of subsequentcontamination with cement or similar materials thereby roviding forretaining the mud at all times in excellent condition in terms of thedesirable properties enumerated hereinabove.

It has been discovered that by, a suitable choice of treatment, not onlycan the viscosity. of a mud, and particularly of a contaminated mud,.becontrolled, but the cake-forming. and water-loss properties of the mud,as measured by thefiltration rate, can also simultaneously be regulatedand maintained. at a high quality. It has further been determined thatcontrolling the viscosity of a mud, and especially of a cement-cut mud,does not necessarily control the filtration rate of the mud.

It is desirable in practicing this invention to improve the performancecharacteristics of a mud not to employ an amount of treating agent oragents in excess of the minimum amount necessary to obtain the desiredperformance characteristics. If the quantity of reagent exceeds thisminimum amount in any great excess the mud may be deleteriouslyaffected. Normally the -reagents are added in relatively smallproportions in the order of about 001% to 2.0% by weight based upon theweight of drilling fluid treated, although under some circumstancesasmuch as by weight or even 10% by weight of some of the reagents may beused. By the application of the above described tests it may readily bedetermined what the necessary amount of any given reagent or reagents isfor any mud.

Before considering the types of reagents comprising the subject matterof this invention, it should first be emphasized that, as might beexpected, naturally occurring clays and the muds prepared from them varyconsiderably in character. For example, they differ in ultimate chemicalcomposition, in amounts and types of colloidal material, and in amountsand types of impurities. Furthermore, the common contaminants which maybecome included in the mud during its use in drilling operations,namely, calcium hydroxide leached from cement, and gypsum, differ intype, one being a fairly strong base and the other a neutral salt. As aconsequence and in view of the complex character of colloidaldispersions, it is only logical to expect that in general theperformance characteristics of muds prepared from clays of differentorigins or even of the same mud contaminated with different ma terials,will not necessarily be affected in exactly the same manner by theaddition of any given treating agent. In spite of these variations ithas been found that the treating agents disclosed in the specificationwhen added in proper amount .will control the performancecharacteristics of various muds within acceptable limits.

The methods employed for making performance tests have been outlined indetail above. In determining the effect of a treating agent or agents ona mud, the procedure employed in the laboratory has been to add thedesired amount of treating agent or agents to the mud followedby athorough agitation of the mixture for one hour prior to the conductingof the performance tests. It will be observed that such a procedurecompletely eliminates any necessity for making a chemical analysis ofthe mud and, as a consequence, it has been found to be the mostpractical method which can be employed in. the field.

It has been discovered that the performance characteristics of a mud andparticularly its water loss properties, can be controlled by theadditionto the mud of a treating agent selected from the group comprising thereaction products resulting from the addition of an amine or ammoniumhydroxide or a basically reacting compound-of .8 an alkali..metal tothe.hydr0lysis productof a Waten-dispersible. gum.

It has also-been discovered that the performance characteristics of a.mud and. particularly its water lossproperties can be controlledby theaddition (to the-mudof a treating agent selected from the groupdescribed immediately above along with a secondtreating agentselected-from the groupcomprising the alkalimetal, amin andammonium-salts of higher.molecular-weight carboxylic acids and oilsoluble .sulfonic acids either. singly or in admixture with one another.

By'the term alkalimetal it is meant to 'include lithium, sodium andpotassium.

By the term basically reacting compound -it is meant to include oxides,hydroxides and other compounds which will react with the acidic productsformed by the hydrolysis of water-disp ersi ble gums to form thecorresponding salts. Y

By the term-amines and ammonium hyd roxide it is meant to include notonlythe hydroxide of the compound known chemically as ammonia, but alsothe various amines and substituted amines such as for example dipropylamine and triethanolamine. I k

The term higher molecularrv'eight carboxylic acids is meant to includethose organicicom pounds of the fatty acid type having rnoretthan aboutcarbon atoms per molecule such as f or example, olcie acid, palmitic acid, li r 1oleic acid, etc. It is also meantto includethose other carboxylic acidsha-ving more than about lo caijbon atoms and closelyrelated to thefatty acidssuch as, for example, thenaphthenic acids .andthe rosin acids such as abietic acid.

Thefsulfonic acids of relativelyhigh molecular weight employed topreparethe oil solubl 1v kali metaland ammonium salts maybethpse syntheticallyproduced or those obtainedfromthe treatment of petroleum fractions. Thelatterare formed when lubricating oilfractions or similiar petroleumfractions are treated with concentrated or fuming sulfonic acid. Theso-called inlia hogany acids dissolve in the .oil phase,,whereas theso-called green acids arethe water-soluble organic acids whichpassintothe sludge. After separation of the sludge the mahoganyacid s which arepreferred may be recoveredin the gform of sodium salts bytreatment ofthe acid-treated oilwith sodium. hydroxide to produce the sodiumsulfonates which are then subsequently removed from the, oil solution byextraction with alcohol. The other alkali metal salts and the ammoniumsalts may bepbtained from theabove sodium salts by well known processesof metathesis. example of. acommercially available oil-soluble alkalimetal salt of a higher, molecular weight sulfonic acid is a concentratein lubricating. Oil, comprising about 60% sodium sulfonates and,,4()%lubricating oil.

Desirably, but not necessarily, the treating agent selected from thegroup comprisingvthe alkali metal and ammoniumsalts. of higher.molecular weight carboxylic acids and oil-soluble sulfonic acids, may bedispersed in a. petroleum orother hydrocarbon oil. such as spray oil, atransformer oil extract produced by Edeleanu extraction of a suitablepetroleum distillate with sulfur dioxide, a light lubricating oil orevena heavy lubricating-oil, prior to introduction into the drilling fluid.

It has further been discovered that the alkali metal and ammonium acidand neutral saltslof the various acids of phosphor-us such asortloophosphoric acid, pyrophosphoric acid, hexametaphosphoric acid, etc.,when added to drilling fluids in conjunction with a treating agentselected from each of the classes of compounds disclosed hereinabove oronly from the first named class of compounds disclosed hereinabove,particularly when the drilling fluid is contaminated with cement orsimilar materials yielding polyvalent metal ions, results in performancecharacteristics which are better than can be obtained by the use ofthese materials alone.

One factor which has not been previously mentioned concerning thechemical treatment of muds is based on the fact that in actualcommercial use muds may be exposed to temperatures of as high as 150 F.to 250 F., the temperature depending principally upon the locationandthe depth at which the drilling is being conducted. It has beenobserved that many muds which have been chemically treated to improvetheir performance characteristics tend to deteriorate with respect tothese characteristics upon prolonged exposure to temperatures in theneighborhood of 200 F. to 250 F., or even lower as is the case indrilling operations. This is apparently due to the fact that thechemicals added may be hydrolyzed or otherwise affected in such a manneras to alter their original efiect upon the performance characteristicsof the mud. It might be thought, therefore, that the use of chemicalsreacting in this way would be a bar to their practical application inthe treatment of muds, and in those cases where the degradation withrise in temperature is rapid, such as in the case of sodiumhexametaphosphate, their use may be inadvisable. However, it has beenfound that many chamicals, which apparently only slowly lose theireffectiveness upon exposure to heat, may be utilized. In such cases itis preferable to add the chemical to the mud each day, therebymaintaining a low filtration rate and a low viscosity. The addition ofthree times as much chemical as is required to maintain the desiredperformance characteristics over a period of one day will not maintainthe performance characteristics over a period of three days. Of course,it is evident that wherever it is feasible, it is preferable to usechemicals whose effect upon the performance characteristics of a mud arenot altered by prolonged exposure to elevated temperatures such as maybe encountered in the particular zone beingdrilled, and if such chemicalwill give the desired performance characteristics according to the testsherein disclosed, such a chemical is the most desirable. In some cases.it has been observed that a certain order of addition will give betterper- 3 formance characteristics than the reverse order of addition. Inthe examples given below, therefore, unless otherwise noted, it will beconsidered that the chemicals are added in the order in which they arelisted, since they give, when added in such order, the most desirableresults.

It has further been discovered that the performance characteristics of asalt base mud, and particularly its water loss properties can becontrolled by the addition to the mud of a treating agent selected fromthe group comprising the reaction products resulting from the additionof an amine or ammonium hydroxide or a basically reacting alkali metalcompound to the hydrolysis product of a water-dispersible gum.

By the term water-dispersible gum it is meant to include, for example,such products as gum karaya, gum sandarac, gum acacia, gum tragacanth,gum arabic, etc.

The water-dispersible gums may be hydrolyzed by dispersing a quantity ofthe gum in water and subsequently heating to a temperature of about 200F. or higher. If it is desired to employ temperatures much in excess of200 F., it will, of course, be necessary to conduct the hydrolysis in anenclosed pressure vessel. The rate of hydrolysis at a given temperaturecan be accelerated by the addition of a small amount of an acid such as,for example, sulfuric, hydrochloric or acetic acids, or of a base suchas caustic soda. After hydrolysis has been completed the reaction massis neutralized with an amine or ammon um hydroxide or a basicallyreacting compound of an alkali metal to a pH value in the neighborhoodof 10 such as would be indicated by a phenolphthalein indicator. Theresulting aqueous solution can then be added as such to the drilling mudfor the control of performance characteristics.

Where it is desirable to ship a minimum weight of treating agent thehydrolyzed and neutralized product may be dehydrated to yield a powder.This powder can subsequently be added to the drilling mud directly, orit can be dispersed in a quantity of water prior to addition to thedrilling fluid.

The following is an example of the preparation of sodium gum karaya.Approximately 300 ml. of water containing 2.5 grams of sodium hydroxidewas heated to 200 F. in a beaker equipped with a stirrer. Whilecontinuing heating, 20 grams of gum karaya was added to the solution andthe mixture stirred until viscous. The stirring must be sufiicient tocause adequate contact of the gum and the caustic soda. The timerequired for the hydrolysis will vary, but usually a, half hour will besufficient to complete the reaction. Subsequent to the hydrolysis, thepH of the product was adjusted to approximately 10 by the addition ofmore caustic soda. If the pH had been above 10 due to the use of anexcess of caustic soda, a strong mineral acid such as hydrochloric acidcould have been added to adjust the pH to the desired value. Theresulting product is the material which has been termed sodium gumkaraya" and comprises one of the treating agents of the presentinvention.

In the practice of this invention in the field, the treating agents mayconveniently be added to the circulating mud stream at a point adjacentto the mud pump suction inlet in the mud sump. Thorough admixture of thethus introduced reagents may be assured by rapid recirculation of themud from the mud sump through a spare slush pump. During treatment, mudsamples may be taken from the circulating mud stream at frequentintervals and tested in order to determine when the desired degree oftreatment has been effected.

The following examples are presented in the nature of illustrations ofthe practical value of the processes of the invention and are not to beconstrued as limiting'the invention in any sense.

Example I A Santa Maria Valley clay was mixed with water to give a,fluid weighing 78.5 pounds per cubic foot. To a given volume of thisfluid was added an equal volume of water in which had been dispersedvarious treating agents and the viscosity and filtration rate weredetermined on each sample by the procedures already described.

Filtration Rate. Marsh ml. 7 Viscosity .500/500, Secs.

Treating Agent Added, Per- Cent by Weight of the Final Drilling Fluid1st Min.

1st Min.

No added treating agent 34. 5 2.0%v a concentrate comprising about 60%of a sodium salt of mahogany sulfonic acids and about 40% of lubricatingoil' 0 2.0% a concentrate comprisingabout 60% of a sodium salt ofmahogany sulionic' acids. and about 40% of lubricating oil 0.1% sodiumgum sandarac ll 2.0% a concentrate comprising about 60% of a sodium saltof mahogany sulfonic'acids and about 40%of lubricating oil- 0.1% sodiumgum karayal e 2.0% sodium'tall oil soap 0.1% gum acacia f 0.5% sodiumpyrophosphate.

1 Tall oil is an article of commerce obtained as a byproduct fromthe-Swedish process for cellulose pulp making Sweet liquor from theprocess separates into two layers, the upper of which is the crude talloil, which may be purified by distillation to yield a productcontainingbothfatty acids and rosin-type acids.

Eatam'ple 'II I The same initial fluid was used as for theex perimentsdescribed in Example I. To seven volumes of this fluid were added threeVolumes of water in one case and in another threevolumes of watercontaining sodium gum karaya; The viscosities and filtration rates ofthese two samples were determinedand are recorded in the followingtabulation:

I Filtration Rate, Treating Agent Added, Per' gggggfi Cent by Weight ofthe Final" 6007500? Dnnmg Flmd Secs. '1st'5 1st 15 Min- (Z No addedtreating agent. 23.5 15 2s b 0.4% sodium gum karayaUU-" 36.5 3.0 6.3

The same fluid was used as for the experiments described in Example I.To agiven volume-oi this fluid was added an'equal volume of water inwhich had been dispersed'various treating agents, and subsequently thedrillingfluid was admixed with 0.7% by weight of hydrated cement. Theviscosities and filtration rates of these samples were-determined andare recorded in the follow-'- ing tabulation:

Filtration Rate, 7 Marsh ml.- Viscosity 500/500; Secs.

Treating Agent Added, Per 1 Cent'by- Weight-of the Final Drilling Fluid1st 15-- Min;

I e 2.0 a concentrate comprising a No added treating agent 22 b- 2.0% aconcentrate comprising about 60% of a sodium salt of mahogany sulfonicacids and about 40% of lubricating oil 0 2.0% a concentrate comprisingabout 60% of a sodium salt of mahogany sulfonic acids and about 40% oflubricating oil 0.5% qucbracho d 2.0% a concentrate co about 60% of asodium salt of mahogany sulionic acids and about 40% of lubricating oil-0.1-% sodium gum sandara about 60% of a sodium 'salt of mahoganysullonic acids and 1 about 40% of lubricating oil 0.1% sodium gumlraraya;

Example IV The same initial fluid was used i'as' for the Fexvi perimentsdesoribed in Example I.: Toiasgiven volume of this fluid was added .anequal volume of 'water in which .was dispersedvarious treat-' ing'agents; Subsequently; 6% by weight? of sodiumchlorideibased on theweight ofthe final drilling fluid," was added. The viscosities andfiltration rates of these samples were determined and 'ar-e recordedin'the following tabulation:

A. drillingfiu.id. was prepared. by mixing: six pounds of a: bentoniteclay Withv ninety-four pounds of" water." To samples of this mudvarioustr'eat-ing agents' were added"- and the-vis cosities andfiltration rates-thendetermined-by the procedures described hereinabove.The data f rom? these several experimentslare :given" in: thefollowingtabula'tion:

3 Marsh" Treating- Agent Added, IEer Cnt by Weight ofthe Final ggDrilling-Fluid Secs. 1st'5 Min..

41 N0 added treating'agents;;. b 1.0% .a concentrate comprising about ofa sodium saltof mahogany stillbnidacids andabout 40% of lubricating oilc 1.0% a concentrate comprising about 60% ofia sodium salt of mahoganysulfonic acids and about 40% of lubricating'oi]; 0.1% gumf acacia l d0.5%sodium pyrophosphate e 1.0% a concentrate comprising about 60% of asodium saltot mahogany sult'onic acids and about 40% of lubricating oi0.1% sodium gum karaya; 0.5% sodium pyrophosphate.

The drilling fluid described in Example Ia com prises a'mixture of SantaMaria Valley clayand water. Although possessing an acceptable (viscosity, it has such a high filtration rate that "it would normally notbe used inxdrilling opera tionsx Theadditionbf as much as 0.5%: byweightoffsodium' pyrophosphate' (a widelyiused treatingagent) toithedrilling mud, asindicated inaExampleif, improved the filtration ratetosome extent but it was still. undesirablyhigh. The additionof- 2.0%byweight ofa concentrate comprising about 60% of asodiumsaltofmahoganysulfonic acids and about 40% .of-lubricatingoil gaveadrillingfiuid havingacceptable performance characteristics (ExampleIb). However, .even better performance characteristics were obtained'byusing, a combination of a concentrate comprising about 60% -of a sodiumsalt of mahogany sulfonic acids and about 40% of lubricatingoilwithsodium gum sandaradsodium gum karaya, or gum acacia as shown 'iIl-EX- ample Ic, Id, and Ie, respectively.

EiltrationjRato', m1. 1

Example III) shows the marked improvement in filtration rate which canbe obtained by the addition of 0.5% of sodium gum karaya alone to adrilling fluid similar to that of Example Ia and having an undesirablyhigh filtration rate.

Example IlIa shows the efiect of cement contamination on the drillingfluid of Example Ia. Example IIIb demonstrates that the addition of aconcentrate comprising about 60% of a sodium salt of mahogany sulfonicacids and about 40% of lubricating oil to the drilling fluid, followedby cement contamination results in material which is still usable fordrilling operations. Examples IIIc, IIId, 111a, and III demonstrate thatthe use of quebracho, sodium gum sandarac, sodium gum karaya, and gumacacia respectively, in conjunction with a concentrate comprising about60% of a sodium salt of mahogany sulfonic acids and about 40% oflubricating oil are all superior to a concentrate comprising about 60%of a sodium salt of mahogany sulfonic acids and about 40% of lubricatingoil alone in overcoming the effects of contamination with cement.

Example IVa shows the eifect on performance characteristics of addingsodium chloride .in appreciable quantities to the drilling fluid ofExample Ia, Example IVb shows that starch (a material presently used forovercoming the efiects of salt in drilling fluids) improves performancecharacteristics but not to an acceptable extent. Examples IVc, Nd, andIVe demonstrate that the compounds comprising the present invention areeffective in controlling the performance characteristics of a salt basemud.

The drilling fluid described in Example Va, comprising a mixture ofbentonite clay and water, possessed good performance characteristics andwould be usable without treatment in the drilling of a well provided, ofcourse, that it did not become contaminated with materials such ascement, gypsum, etc. However, as has already been indicated, the lowerthe filtration rate the more desirable the mud for drilling operations.Example Vb shows that the use of a concentrate comprising about 60% of asodium salt of mahogany sulfonic acids and about 40% of lubrieating oilalone gives some improvement in filtration rate. Example Vd shows that0.5% of sodium pyrophosphate improves the viscosity but has little or noeffect on the filtration rate. Examples V and Ve show that thecombination of a concentrate comprising about 60% of a sodium salt ofmahogany sulfonic acids and about 40% of lubricating oil with gum acaciaand with sodium gum karaya plus sodium pyrophosphate, respectively,gives muds of improved performance characteristics.

Other modifications of this invention which would occur to one skilledin the art may be made, and these are to be considered within the scopeof the invention as defined in the following claims.

We claim:

1. A drilling fluid stable to salines encountered in drilling,comprising water, finely-divided inorganic solids suspended therein, anda treating agent prepared by hydrolyzing a water dispersible gum in awater dispersion at a temperature of at least about 200 F. in theabsence of an oxidizing agent, and neutralizing the product with aneutralizing agent of the group consisting of ammonia, an amine and abasically reacting compound of an alkali metal, said treating agentbeing added in an amount between about 0.01%

14 and 10% by weight of the drilling fluid, suflicient to reduce thefiltration rate of the drilling fluid to less than about 45 ml. in thefirst hour.

2. A drilling fluid according to claim 1 in which the water dispersiblegum is karaya.

3. A drilling fluid according to claim 1 in which the water dispersiblegum is sandarac.

4. A drilling fluid according to claim 1 in which the water dispersiblegum is tragacanth.

5. A drilling fluid according to claim 1 in which the finely dividedinorganic solid is clay.

6. A drilling fluid according to claim 1 which also is contaminated withcement.

'7. A salt base drilling fluid which comprises water, an inorganic saltdissolved therein to the extent of 1 to 10% by weight, finely-dividedinorganic solids suspended therein, and a treating agent prepared byhydrolyzing a water dispersible gum in a water dispersion at atemperature of at least about 200 F. in the absence of an oxidizingagent, and neutralizing the product with a neutralizing agent of thegroup consisting of ammonia, an amine and a basically reacting compoundof an alkali metal, said treating agent being added in an amount betweenabout 0.01% and 10% by weight of the drilling fluid, sufiicient toreduce the filtration rate of the drilling fluid to less than about 45ml, in the first hour.

8. A drilling fluid according to claim '7 in which the inorganic salt issodium chloride.

9. A drilling fluid according to claim 7 in which the inorganic salt issodium chloride and the neutralizing agent is a basically reactingcompound is an alkali metal compound.

10. A composition as claimed in claim 7 which also contains abactericide.

11. A drilling fluid according to claim 7 in which the finely dividedinorganic solid is clay.

12. A drilling fluid comprising water, finely-divided inorganic solidssuspended therein, a first treating agent prepared by hydrolyzing awater dispersible gum in a water dispersion at a temperature of at leastabout 200 F. in the absence of an oxidizing agent, and neutralizing theproduct with a neutralizing agent of the group consisting of ammonia, anamine and a basically reacting compound of an alkali metal, and a secondtreating agent selected from the group consisting of the alkali metal,amine, and ammonium salts of higher molecular weight carboxylic acidsand oil-soluble sulfonic acids and mixtures thereof, said treatingagents being added in amounts between about 0.01% and 10% by weight ofthe drilling fluid sufiicient to reduce the filtration rate of thedrilling fluid to less than about 45 ml. in the first hour.

13. A drilling fluid according to claim 12 in which the second treatingagent is sodium mahogany sulfonate and the gum is gum karaya.

14. A drilling fluid according to claim 12 in which the gum is karaya,the neutralizing agent is a basically reacting sodium compound, thesecond treating agent is sodium mahogany sulfonate, and a third treatingagent consisting of 0.01% to 10% by weight of sodium pyrophosphate isalso employed.

15. A drilling fluid according to claim 12 in which the finely-dividedinorganic solid is clay.

16. A composition as claimed in claim 12 in which the second treatingagent is the sodium compound of oil soluble sulfonic acid (mahoganyacid).

17. A composition as claimed in claim 12 in aar mgagaai whichlxthesecondatreating agentisme reaction Number Name Date. product .ofanvalkaliametal hydroxide and-ztall" 2,174,027 Ball V Sept 26, 19'39'-oil. 2,209,591 Barnes. July 30,1940 PAUL-7W FISCHER; 2,211,688 I ByckAug- 13, 1940 RAYMOND A.-:-ROGERS. 5 2,294,877- Wayne Sepia- 1,- 194212,295,06? Williams Sept.'8,:1942' REFERENCES CITED 2,297,650 Mazee Sept.29,1942 The following references-are of record :in the 2,336,171Freeland 1943' file f t t t- 2,33'h296 Kennedy Dec: 21,1943 102,350;15&= Dawson May 30,1944.

UNITED" STATES PATENTS Number Name Date OTHER REFERENCES 1 2,109,858Cannon .Marz 1,1938 Commercial organic Ana1yses,-A11en,ivo1. 1,3111.

2,129,913 Cross et a1.= "Sept.-.13,- 1938 ed.," page 424, year, 1898.

Certificate of Correction Patent No. 2,518,239 August 15, 1950 PAUL W.FISCHER ET AL.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows:

Column 4- line 6'7 after the Word inor anic insert salt; column 8 line43 for n a. 7 sulfonlc read sulfumc; line 73, after metal insert(17722716,; column 14, hnes 33 and 34, strike out compound 1s an;

and that the said Letters Patent should be read as corrected above, sothat the same may conform to the record of the case in the PatentOfiice.

Signed and sealed this 28th day of November, A. D. 1950.

THOMAS F. MURPHY,

Assistant Oommz'ssz'oner of Patents.

Certificate of (Jorrection Patent No. 2,518,439 August 15, 1950 PAUL W.FISCHER ET AL.

It is hereby certified that error appears in the printed specificationof the above" numbered patent requiring correction as follows:

Column 4, line 67, after the Word inorganic insert saltj column 8; line43, for sulfonic read sulfuric; line 73, after metal insert amine,column 14, lines 33 and 34, strike out i compound is an and that thesaid Letters Patent should be read as corrected above, so that the samemay conform to the record of the case in the Patent Office.

Signed and sealed this 28th day of November, A. D. 1950. v

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

1. A DRILLING FLUID STABLE TO SALINES ENCOUNTERED IN DRILLING,COMPRISING WATER, FINELY-DIVIDED INORGANIC SOLIDS SUSPENDED THEREIN, ANDA TREATING AGENT PREPARED BY HYDROLYZING A WATER DISPERSIBLE GUM IN AWATER DISPERSION AT A TEMPERATURE OF AT LEAST ABOUT 200*F. IN THEABSENCE OF AN OXIDIZING AGENT, AND NEUTRALIZING THE PRODUCT WITH ANEUTRALIZING AGENT OF THE GROUP CONSISTING OF AMMONIA, AN AMINE AND ABASICALLY REACTING COMPOUND OF AN ALKALI METAL, SAID TREATING AGENTBEING ADDED IN AN AMOUNT BETWEEN ABOUT 0.01% AND 10% BY WEIGHT OF THEDRILLING FLUID, SUFFICIENT TO REDUCE THE FILTRATION RATE OF THE DRILLINGFLUID TO LESS THAN ABOUT 45 MI. IN THE FIRST HOUR.